I have a hosting platform running on DNN 5.5.1.22. I recently moved my box from a Windows Server 2003 system to Windows Server 2012 and as part of this, I upgraded the application pool to run in .NET 4.0, Integrated mode.

I ran into this exact same problem but didn't want to be forced into a DNN upgrade until I'm ready to properly roll that out, as it involves testing a handful of custom modules, etc.

So I took a deeper dive and found that the issue here was the preCondition on the handlers section of the web config for LinkClick (as well as a few others) were set to "integratedMode,runtimeVersionv2.0".

My fix to this issue was to simply change 2.0 to 4.0 in the preCondition, but you could also just remove the runtimeVersion portion of the preCondition (so that it's just preCondition="integratedMode").

I hope this helps someone else out there!

Caleb, your post helped me a year and a half after you posted it, and my DNN version is different as well. 6.2.2. Thanks for helping a guy out. - Mark